For example in python:
employees[x][i] = float(employees[x][i]) 
4 Answers
Like most languages, it refers to an element in a multidimensional list:
l = [[0,1,2,3], [1,1,1,1]] l[1] == [0,1,2,3] l[1][2] == 2 
Comments
The two brackets mean you're accessing an element in a list of lists (or dictionaries)
So in this example, it might look something like this
In [17]: employees = {'joe': ['100', 0], 'sue': ['200', 0]} In [18]: x = 'joe' In [19]: i = 0 In [20]: employees[x][i] Out[20]: '100' 3 Comments
LazerSharks
so if i=3, and x=4, you are accessing the fourth element in the third element,which is also a list, in the list employees?
Greg Hewgill
@usmcs: Note that dictionary vs. list is determined by the type of the
employees or employees[x] object, not by whether the thing inside the brackets is a string or an integer. Integers can be dictionary keys, but strings cannot be array indexes.
munk
@GregHewgill Yes, that was a sloppy statement on my part, thanks for the clarification. ShaltNot: I think you have it backwards. In this example, x=4 would be the 4th element of employees and i would be the 3rd element of employees[x]
I put in extra parens to show how this is evaluated
(employees[x])[I] = float((employees[x])[i]) and an example
>>> foo = dict(name="Foo", salary=10.00) >>> bar = dict(name="Bar", salary=12.00) >>> employees = dict(foo=foo, bar=bar) >>> employees {'foo': {'salary': 10.0, 'name': 'Foo'}, 'bar': {'salary': 12.0, 'name': 'Bar'}} >>> employees['foo']['name'] 'Foo' >>> employees['bar']['salary'] 12.0 employees could also be a list (or any other kind of container)
>>> employees = [foo, bar] >>> employees [{'salary': 10.0, 'name': 'Foo'}, {'salary': 12.0, 'name': 'Bar'}] >>> employees[0]['name'] 'Foo' >>> employees[1]['salary'] 12.0 
Comments
Syntax meaning of [] in python:
In python, [] operator is used for at least three purposes (maybe incomplete):
- define in literal an array, like xx = [0,1,2,3]
- array element indexing, like x1 = xx[1], which requires index be integer or evaluated to a integer
- dictionary member retrieval, like s = person['firstname'] // person = {'firstname':'san', 'lastname':'zhang'}, in this case, the index can be anything that a dict tag can be
Thing goes complex when embedding [] in [] or [] next to [], see examples below:
matrix = [[0,1],[2,3]] e01 = matrix[0][1] people = [{'fname':'san','lname':'zhang'}, {'fname':'si', 'lname':'li'}] last1 = people[1]['lname'] [[]] and [][] are reciprocal to each other.
employees[x][i]represents a value,, this syntax will just convert your value tofloatand store it back...